Thermostatic switch



Jan. 16, 1934. G R, TOWNSEND THERMOSTATIC SWITCH Filed July 31, 1930 e n t mo .t W A W m he r Patented Jan. 16, 1934 PATENT OFFICE THERMOSTATIC SWITCH George R. Townsend, Schenectady, N. Y.,

assignor to General Electric Company, a corporation of New York Application July 31, 1930. Serial No. 472,009

Claims. (01. 200138) My invention relates to thermostatic switches and more particularly to those of the typehaving a spirally wound bimetallic thermo-responsive switching element.

In the usual formof such devices one end of the spirally wound. bimetallic thermo-responsive element is fixedly mounted and the free end thereof connected to operate the switch contact between a plurality of circuit controlling positions in response to predetermined variations in temperature.

The principal object of the present invention is to provide an improved construction of thermostatic switch which compensates for the variation in axial length of the spirally wound bimetallic thermo-responsive element upon movement thereof in response to temperature variations so as to effect rotary movement of the switch contact without the possibility of binding or misadjustment of the operating mechanism interconnecting the thermostatic element, with the switch contact.

In the preferred embodiment of my invention I provide a casing which encloses a circuit making and breaking device. A bearing is provided in the casing which permits rotation of the shaft as well as a lateral movement thereof. At one end of the shaft within the casing is frictionally mounted the lever mechanism for operating the circuit making and breaking device. A floating contact is made between the lever mechanism and the circuit making and breaking device whereby only rotary movement is transmitted from the shaft to the circuit making and breaking device. The

' spiral thermostatic strip is fastened to the outside of the casing and to the other end of the rotatable shaft. As the thermostatic strip expands and contracts in response to the heating conditions the shaft has both a rotating movement and a lateral movement. Since the shaft is not placed under tension or compression the undesirable friction existing betweenthe shaft and the bearing is eliininated which results in smooth operation of the switching mechanism.

Referring to the drawing, Fig. 1 shows a crosssection of my thermostatic switch taken on the line A-A of Fig. 2 and Fig. 2 shows the details of the circuit making and breaking portion of my thermostatic switch.

A -casing for enclosing the circuit making and breaking device is provided with a removable cover 11. The circuit making and breaking device is mounted upon a base 12 of insulating material which is fastened to the casing 10 by suitable screws. A stationary contact 13 cooperates with the movable contact 14 resiliently mounted upon the spring element 15 which in turn is mounted on the bracket 16 fastened to the base 12. A stop member 1'7 is provided for the movable contact 14. As can be seen the stop member is adjustable.

By means of this construction the time required for closing the movable contact in response to the action of the thermostatic element can be varied. This is at timesdesirable.

The casing is provided with a bearing 19, the rotatably and slidably supporting shaft 18. At the inner end of the shaft 18 is frictionally mounted the lever 20 provided with the pin 21 which cooperates with the U-shaped portion of the resilient member 15 to move the movable contact 14 of the circuit making and breaking device. This construction permits both a lateral and a parallel motion of the shaft with respect to the circuit making and breaking device yet transmits only the rotary movement to the circuit making and breaking device. The lever 20 is mounted between the washer 22 keyed to the shaft 18 and the washer 23 which is spring-pressed against the lever 20 by means of the spring 24 held in place by means of the washer 25. Thus when the movable contact has reached either of its positions, that is, its closed position or its open position, against the stop 1'7, the shaft 18 may continue to rotatein response to the contraction or expansion of the thermostatic strip 2'7 without exerting undue strain upon the lever and the circuit making and breaking mechanism.

A bridging member 26, which is broken in Fig. 2 to show the pillar 31, is removably supported by a pair of pillar members and 31 to provide a bearing for the end of the rotatable shaft 18.

Bearing 19 and member 26 thus provide a sturdy and effective double bearing support within the casing for the long shaft 18 and while permitting free rotation and sliding movement of the shaft insure proper alignment of the shaft at all times during operation. The member 26 being removable permits easy disassembly of the shaft and frictionally mounted switch operating arm for repair or inspection. A bimetallic strip 2'7 of spiral form is rigidly fastened to the outside of the casing by means of a screw 29. The other end of the spiral strip is fastened to the outer end of the rotatable shaft by means of the screw Theoperation of the device is as follows: With the parts as shown in Fig. 2 with the movable contact 14 closed upon the stationary contact 13, when the bimetallic strip expands due to heating conditions resulting from the operation of any heating apparatus (not shown) controlled by the switching mechanism the bimetallic strip twists and thus causes rotation of the shaft 18 in a counter-clockwise manner. The'pin 21 cooperating with the resilient supporting element 15 moves the movable contact 14 out of engagement with the stationary contact and against the stop 1'7. After the resilient element 15 has come into contact with the stop 1'7 further rotation of the lever 20 is prevented. If the bimetallic strip should continue to.expand the shaft 18 will rotate in response thereto without effecting a further operation of the circuit making and breaking device, since the lever 20 will slip with respect to the shaft.

Since the bimetallic strip as it is being heated tends to expand laterally the shaft 18 will also move in a lateral direction so that as the bimetallic strip responds to heating conditions the rotatableshaft has both a lateral and a rotating movement which permits a smooth operation of the circuit making and breaking device. The connection between pin 21 and the circuit making and breaking device permits the lateral movement of the shaft without affecting the proper operation of the circuit making and breaking device. Upon cooling, the reverse operation takes place and due to the frictional engagement be-' tween the rotatable shaft 18 and the lever 20 immediately upon reverse rotation of the shaft the circuit making and breaking device will be operated to cause closing of the contactors l3 and 14.

It will'thus be seen that by means of my novel supporting means for the rotatable shaft I provide a thermostatic switch in which the operation is smooth and accurate.

The embodiment of the invention illustrated and described herein has been selected for the purpose of clearly setting forth the principles involved. It will be apparent, however, that the invention is susceptible of being modified to meet the different conditions encountered in its use, and I, therefore, aim to cover by the appended claims all of the modifications within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A thermostatic switch having a casing, a bearing in said casing extending through a wall thereof, a shaft supported in said bearing and extending within said casing, a contact supporting base mounted within said casing on said wall adjacent said shaft, a stationary contact mounted on said base, a stop member mounted on said base and oppositely .disposed to said stationary contact, a movable member carrying a contact for cooperating with said stationary contact and mounted to move between said contact and said stop member, a cut-away portion in said base between said stationary contact and said stop member, an arm frictionally mounted on said shaft withinrsaid casing and having a pin connected to operate said movable member and extending within the cut-away portion of said base and movable therein whereby a compact switch mechanism is obtained, and a spiral thermostatic element having one end fixed to said casing and the other end attached to the exterior end of said shaft for operating the same.

2. A thermostatic switch provided with a casing having a bearing therein extending through a wall thereof, a shaft slidably and rotatably mount ed in said bearing and extending within said casing from the exterior thereof, a thermostatic element connected to said casingand to the exterior end of said shaft for rotating the same in response to temperature changes, a base in said casing mounted on said wall adjacent said shaft and supporting a switch mechanism, a cut-away portion in said base adjacent said switch mechanism, an arm frictionally mounted on said shaft within said casing and having a pin extending therefrom for operating said switch'mechani'sni, said arm extending within said cut-away portion and movable therein whereby a compact switch mechanism is obtained, and a second bearing mounted within said casing for slidably and rotatably supporting the end of said shaft within said casing.

3. A thermostatic switch having a stationary contact, a resilient member having a U-shaped portion for movably supporting a contact cooperating with said stationary contact, an adjustable stop for said resilient member, a shaft, bearings for said shaft for rotatably and slidably supporting said shaft, a spiral thermostatic element having one end fixed and the other end attached to one end of said shaft, a member frictionally mounted at the other end of said shaft between said bearings and carrying a pin, said pin engaging in the U-shaped portion of the resilient member for moving the contact carried thereby to open and close on'the other contact by transmitting only the rotary motion of said shaft as the thermostatic strip expands and contracts in response to temperature changes, said adjustable stop being operable to vary the time required for' moving said resilient member to close said movable contact on said stationary contact in response to action of said thermostatic element.

4. A thermostatic switch having a casing, a switch mechanism therein, said mechanism including 'a stationary contact and a resilient member movably supporting a contact for cooperation with said stationary contact, a shaft, a bearing ext-ending through said casing for slidably and rotatably supporting said shaft, a second bearing in said casing for slidably and rotatably supporting the end of said shaft and spaced from said first bearing, said shaft extending from the inside of said casing to ,the exterior thereof, a thermostatic spiral element having one end fixed to said casing and the other end to the outside end of said shaft, an arm frictionally mounted on the inside end of said shaft between said bearings and a pin on said arm for engaging said resilient member to open and close said contacts by transmitting only the rotary motion of said shaft when said thermostatic element expands and contracts in response to temperature changes.

5. A thermostatic switch having a casing, a switch mechanism within said casing including a stationary contact and a resilient member having a U-shaped portion carrying a contact movable toward and away from said stationary contact, a pair of bearings in said casing, one of said bearings extending through the side of said casing, and another of said bearings being spaced therefrom within said casing, a shaft rotatably and slidably supported in said bearings and extending through said casing to the exterior thereof through said one bearing, a spiral thermostatic element having one end connected to the exterior of the casing and the other end to the exterior end of said shaft,,an arm frictionally supported on said shaft between said bearings said bearings maintaining said shaft in alignment during operation of said shaft and switch mechanism, said arm carrying a pin engaging said resilient member in its U-shaped portion to transmit only the rotary movement of said shaft when said thermostatic element in response to temperature variations expands and contracts to open andclose said contacts.

GEORGE R. TOWNSEND. 

